手持终端的两根通讯线有极性吗

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求助：手持终端的两根通讯线到底有极性吗？刚进公司的时候师父说没有极性，可以随便接，但是看有的题目上说是有极性的，请大神指导一二谢谢！

hzf

我们考试也考过，没有正负之分的！实验确实能让人记忆深刻！

liusha

王天泽 发表于 2016-12-14 13:24
在实际工作中是没有极性的，你可以看看手操器的说明书（375）。你也可以在现场实际测试。
在考试中，都是给 ...

这两天公司正好正组织年底考试  上面有道题是关于475的 不过给的也是没有极性

黄河入海口石头

375.475都没有极性，找不到串联250欧姆电阻即可，还有就是别把现场总线的拨过去，闹过笑话的

舞长安

Connect the 375 Field Communicator with the appropriate connectors in parallel with the instrument or load resistor. The HART connections are not polarity sensitive.
使用适当的连接器将375现场通讯器与仪器或负载电阻并联。 HART连接不对极性敏感。
In order for the 375 Field Communicator to function properly, a minimum of 250 ohms resistance must be present in the HART loop. There are three terminals on the top of the 375 Field Communicator.
为了使375现场通讯器正常工作，HART回路中必须至少存在250欧姆的电阻。 375现场通讯器顶部有三个端子。
Two of them are red and one of them is black. Each red terminal is a positive connection for its protocol. The black terminal is a common shared by both protocols. There is an access door to ensure that only one pair of terminals is exposed at any one time; see Figure 3-1. There are several markings to indicate which pair of terminals is for which protocol.
其中两个是红色的，其中一个是黑色的。 每个红色端子是其协议的正连接。 黑色终端是两种协议共享的。 有一个检修门，以确保只有一对端子在任何时间暴露; 参见图3-1。 有几个标记来指示哪一对终端是哪个协议。

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小小虫 发表于 2016-12-15 07:08
试过是不错的学习方法。

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王天泽 发表于 2016-12-14 13:49
375用户手册上面有这样几段话：
Connect the 375 Field Communicator with the appropriate connectors in  ...

谢谢天泽师父

小小虫

试过是不错的学习方法。

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嗯嗯，现场试过没有极性

王天泽

375用户手册上面有这样几段话：
Connect the 375 Field Communicator with the appropriate connectors in parallel with the instrument or load resistor. The HART connections are not polarity sensitive.
In order for the 375 Field Communicator to function properly, a minimum of 250 ohms resistance must be present in the HART loop.
There are three terminals on the top of the 375 Field Communicator. Two of them are red and one of them is black. Each red terminal is a positive connection for its protocol. The black terminal is a common shared by both protocols. There is an access door to ensure that only one pair of terminals is exposed at any one time; see Figure 3-1. There are several markings to indicate which pair of terminals is for which protocol.